1. Field of the Invention
The present invention relates generally to high voltage switches and more particularly to high voltage switches where a circuit breaker is connected in series with a disconnect switch mounted in an enclosure.
2. Description of the Prior Art
High voltage transmission line systems are necessarily provided with power switching means for connecting or disconnecting the transmission lines from a source of power to a load. The power switching means commonly takes the form of a circuit breaker which is adapted to automatically break a circuit when a fault is sensed, and a disconnect switch, such as a knife switch, which is connected in series between the circuit breaker and the load. Unlike a circuit breaker, a knife switch is not adapted to repeatable break a high voltage circuit but can be used to isolate the load from the transmission line to allow for maintenance. Due to the high electrostatic potentials involved, the switches are commonly substantial in size and mounted within an enclosure such as a cabinet and various safety devices are used to terminate power within the enclosure prior to or upon opening for maintenance.
Knife switches commonly comprise a movable blade or arm controlled by a linkage which may be operated manually, or by electric, pneumatic or hydraulic means. Ordinarily the elements of the switch are exposed, the movable blade portion being pulled free of engagement with the stationary contact portion and swinging through a large arc to effect opening of the switch. Such a disconnect switch is commonly known in the art as a "knife" switch. An example of a knife switch is shown in U.S. Pat. No. 4,541,033, the disclosure of which is hereby incorporated by reference.
Enclosures have been utilized to physically protect the circuit breaker and the knife switch where a mechanical latching mechanism is used to open the knife switch to disconnect the circuit breaker from the input power transmission line. Such an arrangement is shown in U.S. Pat. No. 3,896,353 the disclosure of which is hereby incorporated by reference. The mechanical latching mechanism simultaneously unlatches an access door to the enclosure and operates the knife switch to isolate the circuit breakers and other elements within the enclosure from the transmission line so that maintenance can be safely effectuated.